Cutting tools for modern machining centers are generally chucked in tool holders and connected to the work spindles of the machining centers by means of these tool holders. The concentricity of the unit consisting of the cutting tool and the tool holder is subject to high requirements. It is therefore common for the tool holders to be balanced after chucking a new tool.
Balancing takes place on balancing machines in which the tool holders are set into rotation together with the tool inserted into them. The forces generated by the still-present unbalance are recorded precisely and provide exact information with regard to the position and extent of the unbalance.
As standard, the tool holders are inserted into the spindle of the balancing machine and then set into rotation about their operating axis, whereupon a measurement is made once by which the extent and the position of the unbalance are then determined.
A so-called index measurement is made where the highest possible degree of precision is to be ensured in balancing.
Within the context of such an index measurement, the tool holder is installed into the spindle in a first position and then set into rotation by the spindle. In the process, a first measuring cycle is carried out. Then, the balancing machine is stopped and the tool holder is installed in the spindle in a second position, which is most frequently turned by 180 degrees relative to the spindle, which is generally done manually. The spindle is now set into rotation again and a second measuring cycle is carried out. With the measured values obtained in these two measuring cycles, the position and the extent of the unbalance can be determined particularly precisely.
The manual reinstallation is labor-intensive, time-consuming and, at least in some cases, also detrimental to precision. This becomes clear if one brings to mind the fact that, for various reasons, it may happen every now and then that the tool holder, due to being detached from the spindle and reinserted at a later point in time, does not come to lie quite in its ideal position anymore, which it had during the first measuring cycle, or vice versa.
In order to keep manpower requirements as low as possible, the idea has already been contemplated internally that the tool holders not be relocated manually, but that an industrial robot associated to the balancing machine be used for this purpose, which imitates the manual manipulation, but works more quickly and with greater precision. Whether this idea was already published somewhere else is not known to the applicant.
Be that as it may be, such a solution is disadvantageous because it requires great machine expenditure and because it cannot be ruled out completely also in this case that placement deviations of the tool holder occur during reinstallation. The use of an industrial robot associated with the balancing machine is also unsatisfactory with regard to cycle-time reduction because the arm of such an industrial robot loses a considerable amount of time during each cycle already due to the fact that it has to be driven towards the tool holder with a multi-axis movement and later retracted. Moreover, a robot arm with access from the outside requires the protection hood to be opened and closed again during each access, which also costs time or increases the machine expenditure.
In view of this, it is the object of the invention to provide a balancing machine by means of which an index measurement can be carried out quickly and with little effort.